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Ok, I have a set of G4 speakers, the Apple Pro ones, (I'm a tech guy at a school) that need to be modified for use in a regular Mac (ie non-G4). Obviously the plug won't work with a normal 3.5mm mini socket, so I'm thinking about splicing the cord apart and making it go into a regular 3.5mm mini and a Firewire plug to supply the power. However, I don't know what voltage the speakers require. I'm thinking it's 30v because the now-discontinued Griffin iFire used Firewire for power (at least, I think it used it for power), which is also 30v (without a load).

The Apple Pro speaker are passive speaker, that means they have no integrated amplifier, and therefore need to be hooked up an amplifier (the Pro speaker connector on the iMac G4 and PowerMac G4 since the Digital audio is an amplified sound output).

This also means they don't need any power per se...without an amp, you won't hear much when connecting them to a regular line out. And you certainly would fry them by connecting them to the Firewire power pins.

The iFire has an integrated amp for the Pro speaker.

$60 seems a bit hefty for the iFire...you should find it around $30-40 max.

The Apple Pro speaker are passive speaker, that means they have no integrated amplifier, and therefore need to be hooked up an amplifier (the Pro speaker connector on the iMac G4 and PowerMac G4 since the Digital audio is an amplified sound output).

This also means they don't need any power per se...without an amp, you won't hear much when connecting them to a regular line out. And you certainly would fry them by connecting them to the Firewire power pins.

The iFire has an integrated amp for the Pro speaker.

$60 seems a bit hefty for the iFire...you should find it around $30-40 max.

Ok i tried this:

Hooked the speaker wires up to a mini jack. No problems with playback, but as you said, it was really quiet. Then I took off the firewire plug to try this next thing:

So I went to Radio Shack to get a 18 watt AC adapter (12 volt x 1500mA) because I found that the speakers need a combined 20 watts of power. Yes, I know 18 isn't 20, but it should still be close. Anyway, I tried hooking the power wires from the speakers to the AC adapter. Nothing happened. No amplification, no nothing. Seems illogical. Unless I did somethign wrong.

Hooked the speaker wires up to a mini jack. No problems with playback, but as you said, it was really quiet. Then I took off the firewire plug to try this next thing:

So I went to Radio Shack to get a 18 watt AC adapter (12 volt x 1500mA) because I found that the speakers need a combined 20 watts of power. Yes, I know 18 isn't 20, but it should still be close. Anyway, I tried hooking the power wires from the speakers to the AC adapter. Nothing happened. No amplification, no nothing. Seems illogical. Unless I did somethign wrong.

How would I amplify the signal? The computer can't amplify it enough.

Ok, I think you did misunderstand what I meant...
The Apple Pro Speaker are passive speaker. That means thay have no audio amplifier. In the iMac G4 (and the PowerMac G4 since the Digital Audio) there is a 20W audio amplifier built in, which hooks up to the Pro speaker through that special Apple connector.
Now, the audio out of any other Mac than those I described before is a line out. Line level sound signals need to be amplified.
There is no amplifier in the Pro speaker, and there are no power wires either. They only have left and right audio signal, ground (possibly splitted, so one ground per signal) and some kind of circuitry so the computer will recognise them as Pro speaker (no idea why that is needed, as there are no other speaker with that kind of connector).

Ok, I think you did misunderstand what I meant...
The Apple Pro Speaker are passive speaker. That means thay have no audio amplifier. In the iMac G4 (and the PowerMac G4 since the Digital Audio) there is a 20W audio amplifier built in, which hooks up to the Pro speaker through that special Apple connector.
Now, the audio out of any other Mac than those I described before is a line out. Line level sound signals need to be amplified.
There is no amplifier in the Pro speaker, and there are no power wires either. They only have left and right audio signal, ground (possibly splitted, so one ground per signal) and some kind of circuitry so the computer will recognise them as Pro speaker (no idea why that is needed, as there are no other speaker with that kind of connector).

No, I understand you

I'm aware that they have no audio amplifyer. They only came with that stupid proprietary plug, which has 4 rings and a collar with an inside and an outside. When you cut the plug off, there are 6 wires - 2 for audio ground, and 1 for left and another for right audio. The other two I assume (since they're red and black) are the 20w power, which connect to the collar on the plug (tested with an ohmeter, so I know that for a fact). I'll post the pinout once I get home and can upload it to Photobucket.

As I said, I tried to use that 20w AC adapter from Radio Shack to plug into the red and black wires. It seems logical to me that those are for power, as they would hook up to a power conduit when plugged into a G4. And they're red and black

Why would the red and black wires be power wires? As passive speakers, there's nothing to power.
Where did you get the 30V information from? Would be very interesting to know, as I've never seen that...not even in any Apple document to which I have acces as a certified technician.

So if you can tell me where you got that info from, I'd appreciate.

I know that there is some sort of circuitry in the speaker that makes them recognisable as Apple Pro Speaker to the Mac in which they are plugged.

But there definitely is no need to put any power on those wires, there is absoultely no amplification circuitry inside the Apple Pro Speaker.

The 30v came from the fact that the iFire has a firewire output, which is also 30v. Seemed logical at the time. What would the red and black wires be for then? Power is the only thing that makes sense to me.

So the amplifier built in to the G4 - I assume that's on the same line as the audio outs then? Blargh again.

Any ideas on how I could get those speakers to work, fully functional with the 20 watts of power? Either that or I can wire them into some RCA plugs and add them to my stereo surround at home

The iFire is nothing else than an external amplifier. It has three ports: 1x Firewire, 1x 3.5mm mini jack audio in (line level) and the special 2.5mm mini jack for the Pro Speaker.

As far as I know, the FW connector is used ONLY to power the iFire, it get's it's audio signal from the standard 3.5mm Line in. Which is why the iFire can be used with any Firewire equipped computer, including PCs, without any necessary drivers.

So, again, there is no way of getting any convenient sound out of those speakers unless you hook it up an amp, either by re-soldering the Apple connector and buying an iFire, or by soldering a 3.5mm jack to the audio wires (you can attach both grounds on the single ground pin of a 3.5mm jack) and connect it to a headphone amp (quite more expensive than the iFire).

Unless you have an amp with no more than 20W of power, I wouldn't hook them up to your home stereo...turning up the volume on a more powerfull amp will definitely kill the Pro Speakers...